1. Technical Field
The invention relates to the field of signal processing generally and, more particularly, to a method and circuit apparatus for checking the authorization of access to a signal processing system from designated peripheral units.
2. Description of the Prior Art
Peripheral units are connected to a signal processing system for the purpose of transmitting and, if the occasion arises, receiving signals by means of a code number allocated to each peripheral unit and by means of identification data freely selectable for the respective peripheral units. Signal processing systems which can be accessed from peripheral units are frequently provided with units which, in the event of an intended access from a peripheral unit connected to such a signal processing system, first of all check the access authorization of the relevant peripheral unit. Such a signal processing system can, for example, be found in private and public communications systems as well as in data processing systems which offer specific services to external subscribers. The examination of access authorization, similar to the subscriber identification in a videotex system known from German No. OS 28 42 777, can be performed, e.g., in such a way that a specific code number, for example, a specific calling number, is allocated to each of the peripheral units. In the event of an intended access, the specific number is transmitted from a peripheral unit to the signal processing system, together with freely selectable identifcation data for the particular peripheral unit. An examination of the access authorization by means of said code number and the associated identification data, however, has the disadvantage that forgeries--in particular, through repeated manipulation--of code numbers and the associated identification data cannot be precluded.